Scanner having a light beam incident position adjusting device

ABSTRACT

A scanner is provided that has a light-beam emitter for emitting a light beam, a light-beam deflector for deflecting the light beam to scan a scanning surface, a photo-detector provided at a position outside an image-forming scanning range of the scanning surface to detect a scanning light beam before the scanning light beam starts generating a scanning line in the image-forming scanning range, a rotatable member located in front of an incident surface of the photo-detector and positioned in a recess formed on an outer surface of a housing. The rotatable member is rotatable about a rotational axis perpendicular to a plane defined by the scanning light beam by said deflector. The scanner also has an optical member provided on the rotatable member that allows the scanning light beam to pass therethrough to be incident upon the incident surface of the photo-detector, and a device for adjusting rotational position of said rotatable member about said rotational axis. A through hole through which the optical member is inserted in the housing is formed at the bottom of the recess, and the optical member is inserted into the housing through the through hole.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/098,544, filed Mar. 18, 2002 now U.S. Pat. No. 6,768,568, which is adivisional of U.S. patent application Ser. No. 09/271,455, filed Mar.18, 1999, now abandoned, the disclosures of which are expresslyincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a scanner in which a light beam isdeflected to scan a scanning surface, and more specifically to a scannerwhich is provided with a device for adjusting an incident position of alight beam on a photo-detector used for determining the timing ofcommencement of writing each scanning line with respect to a scanningsurface.

DESCRIPTION OF THE RELATED ART

A laser-beam printer provided with a laser-beam scanner is well known.In a laser-beam printer, a laser beam which is modulated in accordancewith image signals to be output from a laser-beam emitter is deflectedby a polygon mirror to scan a photoconductive surface of aphotoconductive drum in the main scanning direction to thereby form amain scanning line in the photoconductive surface. The laser emission isturned ON and OFF ion accordance with given image signals to draw acorresponding image (charge-latent image) on the photoconductive surfaceof the drum and subsequently this image drawn on the photoconductivesurface of the drum is transferred to plain paper according to aconventional electrophotographic method. Dry powder (e.g., toner) thatadheres only to the charged area is applied to the drum, transferred tothe plain paper and fused by heat. Such a laser-beam printer is widelyused; e.g., as an output device for a computer.

In a laser-beam scanner provided in such a laser-beam printer, aphoto-detector (i.e., a laser-beam detector is generally fixed at aposition outside the latent-image-forming scanning range to detect thescanning laser beam before it starts generating each scanning line. Thephoto-detector generates a pulse signal each time the scanning laserbeam is incident on the photo-detector. The pulse signals output fromthe photo-detector are input to a processor, and subsequently theprocessor generates corresponding horizontal synchronizing pulses(HSYNC) to determine the timing of commencement of writing main scanningdata, namely, writing each main scanning line.

In such a laser-beam scanner, two types of devices for adjusting thetiming of commencement of writing each main scanning line with respectto the photoconductive surface of the drum (i.e., for adjusting thetiming of generating horizontal synchronizing pulses) are known. In eachtype of adjusting device, a reflecting mirror is arranged at a positionoutside the latent-image-forming-scanning range to detect the scanninglaser beam before it starts generating each scanning line, while aphoto-detector is arranged at a position on the path of the laser beamreflected by the reflecting mirror. In one type of adjusting device, thereflecting mirror is rotatable so that the incident position of thelaser beam on the photo-detector can be adjusted, which makes itpossible to adjust the timing of generating horizontal synchronizingpulses. In the other type of adjusting device, the reflecting mirror isfixed while the photo-detector is linearly movable so that the incidentposition of the laser beam on the photo-detector can be adjusted.

In the former type of adjusting device, although the incident positionof the laser beam on the photo-detector can be adjusted by rotating thereflecting mirror, it is difficult to finely adjust the incidentposition of the laser beam on the photo-detector. Furthermore, thereflective mirror needs to be accurately and precisely positioned on abase on which the reflective mirror is to be mounted. In the latter typeof adjusting device, the position at which the photo-detector is to bearranged is quite limited. Moreover, in each type of adjusting device,in the case where the base on which the reflective mirror and thephoto-detector are mounted is slightly deformed after a long period ofuse, the respective positions of the reflective mirror and thephoto-detector deviate from their original positions. In this case, therespective positions of the reflective mirror and the photo-detectorcannot be easily adjusted from outside the laser-beam apparatus.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a scanner provided witha device for adjusting the incident position of a light beam on aphoto-detector used for determining the timing of commencement ofwriting each scanning line with respect to a scanning surface, whereinthe adjusting device makes it possible to finely and easily adjust theincident position of the light beam on the photo-detector.

Another object of the present invention is to provide a scanner havingsuch an adjusting device which makes it possible to finely and easilyadjust the incident position even from outside the scanner.

Other aspects, objects and advantages of the present invention willbecome apparent to one skilled in the art from the following disclosureand the appended claims.

According to an aspect of the present invention, there is provided ascanner including a light-beam emitter for emitting a light beam; alight-beam deflector for deflecting the light beam to scan a scanningsurface; a photo-detector provided at a position outside animage-forming scanning range of the scanning surface to detect ascanning light beam before the scanning light beam starts generating ascanning line in the image-forming scanning range; a rotatable member,located in front of an incident surface of the photo-detector, that isrotatable about a rotational axis perpendicular to a plane defined bythe scanning light beam by the deflector; an optical member, provided onthe rotatable member, that allows the scanning light beam to passtherethrough to be incident upon the incident surface of thephoto-detector; and a device for adjusting rotational position of therotatable member about the rotational axis.

Preferably, the light-beam deflector includes a polygon mirror.

Preferably, a signal, output from the photo-detector, is used fordetecting the timing for commencement of writing the scanning line withrespect to the scanning surface.

The optical member can include a cylindrical lens or a plane-parallelplate. Preferably, the optical member includes a member having anoptical axis which lies in a plane defined by the scanning light beam,and the rotational axis extends perpendicular to the optical axis.

The rotatable member can be positioned in a recess formed in a housingto be rotatable about the rotational axis.

In an embodiment, the recess is a circular recess, and the rotatablemember includes a disc portion which is fitted into the circular recessto be rotatable about the rotational axis.

Alternatively, the rotatable member includes a shaft coaxial to therotational axis, and the rotatable member is positioned in the recesswith the shaft being inserted into a hole formed at the bottom of therecess so that the rotatable member is rotatable about the shaft.

Further, the recess can be formed on an outer surface of the housing,and a through hole through which the optical member is inserted in thehousing is formed at the bottom of said recess, and the rotatable memberis positioned in the recess with the optical member being inserted intothe housing through the through hole.

For holding the rotatable member at an adjusted position, the adjustingdevice can include at least one set screw which penetrates into therotatable member through a slot formed thereon to be screwed into thehousing.

Alternatively, it is possible that the adjusting device includes amember, fixed to the housing, for pressing the rotatable member againstthe bottom of the recess. Preferably, the pressing member includes aspring. Further, the spring can be a leaf spring fixed to the housing byat least one set screw.

Preferably, the scanner further includes a device for rotating therotatable member about the rotational axis.

In an embodiment, the rotating device includes a radial slot formed onthe rotatable member to extend in a radial direction thereof; and arotating tool engageable with the rotatable member to rotate therotatable member about the rotational axis. Namely, the tool includes anengaging pin engageable with the radial slot, an axis of the engagingpin deviating from a rotational axis of the rotating tool.

Alternatively, the rotating device includes a circumferential gearformed on an outer peripheral surface of the rotatable member; and arotating tool engageable with the rotatable member to rotate therotatable member about the rotational axis. Namely, the rotating toolincludes a pinon gear which is engaged with the circumferential gear.

It is preferable that the scanning surface is a photoconductive surfaceof a photoconductive drum.

In an embodiment, the photo-detector and the light-beam emitter aresupported on a common circuit substrate and do not relatively move.

The scanner can include an fθ reflecting lens that reflects the scanninglight beam deflected by the light-beam deflector to the scanningsurface.

According to another aspect of the present invention, there is provideda scanner including a light-beam emitter for emitting a light beam; alight-beam deflector for deflecting the light beam to scan a scanningsurface; a photo-detector provided at a position outside animage-forming scanning range of the scanning surface to detect ascanning light beam before the scanning light beam starts generating ascanning line, the photo-detector generating an output signal upondetecting the scanning light beam to determine a timing of commencementof writing the scanning line with respect to the scanning surface; andan optical member for deflecting the scanning light beam to be incidenton the photo-detector in a direction to vary the timing of the scanninglight beam incident upon the photo-detector.

The present disclosure relates to subject matter contained in JapanesePatent Application No. 10-92725 (filed on Mar. 19, 1998) which isexpressly incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in detail with referenceto the accompanying drawings in which:

FIG. 1 is a perspective view of the scanning optical system of alaser-beam scanner to which the present invention is applied;

FIG. 2 is a perspective view of an embodiment of a device for adjustingthe rotational position of a cylindrical lens with respect to a housingof the laser-beam scanner;

FIGS. 3A and 3B are explanatory views of the cylindrical lens whenrotated about a rotational axis;

FIG. 4 is a perspective view of the scanning optical system of alaser-beam scanner in which a photo-detector and a light-beam emitterare supported on a common circuit substrate;

FIG. 5 is an exploded perspective view of another embodiment of thedevice for adjusting the rotational position of the cylindrical lens;

FIG. 6 is a plan view of still another embodiment of the device foradjusting the rotational position of the cylindrical lens;

FIG. 7 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

FIG. 8 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

FIG. 9 is a plan view of yet another embodiment of the device foradjusting the rotational position of the cylindrical lens;

FIG. 10 is a perspective view of an embodiment of a device for rotatingthe cylindrical lens; and

FIG. 11 is a perspective view of another embodiment of the device forrotating the cylindrical lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the scanning optical system of a laser-beam scanner towhich the present invention is applied. The laser-beam scanner scans thephotoconductive surface of a photoconductive drum 1 (scanning surface).The laser beam scanner and the photoconductive drum 1 are positionedwithin a laser-beam printer as essential elements.

The scanning optical system of the laser-beam scanner is provided with alaser diode (light-beam emitter) 2, a collimating lens 4 a, acylindrical lens 4 b, a reflecting mirror 6, a polygon mirror(light-beam deflector) 8, an fθ reflecting lens 10, an fθ lens 12, areflecting mirror 14, a cylindrical lens (optical member) 16, and alaser-beam detector (photo-detector) 18. The collimating lens 4 a andthe cylindrical lens 4 b together constitute an optical system 4 for thelaser diode 2.

The laser diode 2 outputs a laser beam L1 modulated in accordance withimage signals. The laser beam emitted from the laser diode 2 iscollimated through the collimating lens 4 a. Thereafter, this collimatedlaser beam is made incident upon the cylindrical lens 4 b positioned infront of the collimating lens 4 a. The cylindrical lens 4 b has power inthe sub-scanning direction, so that the spot of the laser beam incidentthereon is converged therethrough in the sub-scanning direction to beincident upon the reflecting mirror 6. The laser beam which is incidenton the reflecting mirror 6 is reflected thereby to be incident on thepolygon mirror 8. The polygon mirror 8 is driven to rotate at a fastrotational speed by a motor (not shown), so that the laser beam incidenton the polygon mirror 8 is deflected in the main scanning direction tobe incident on the fθ reflecting lens 10.

The deflected laser beam L2 which is incident on the fθ reflecting lens10 to be reflected thereby proceeds to the reflecting mirror 20 throughthe fθ lens 12, which is arranged to face the fθ reflecting lens 10.Subsequently, the laser beam incident upon the reflecting mirror 20 isreflected thereby towards the photoconductive surface of the drum 1.

The polygon mirror 8 rotates in a counterclockwise direction (shown byan arrow “A”), as viewed in FIG. 1. The reflecting mirror 14 is fixed ata position to receive the scanning laser beam emitted from the polygonmirror 8 before the scanning laser beam is incident on the fθ reflectinglens 10 at each scanning sweep while the polygon mirror 8 rotates. Thelaser beam L3 reflected by the reflecting mirror 14 is incident on thelaser-beam detector 18 through the cylindrical lens 16. The laser-beamdetector 18 is fixed at a position facing to the reflecting mirror 14with the cylindrical lens 16 being positioned between the reflectingmirror 14 and the laser-beam detector 18. Namely, the cylindrical lens16 is located in front of an incident surface of the laser-beam detector18.

The laser-beam detector 18 outputs a pulse signal for detecting thetiming of commencement of writing each scanning line with respect to thephotoconductive surface of the drum 1 each time the laser beam L3 isincident on the laser-beam detector 18.

As shown in FIG. 2 the cylindrical lens 16 is fixed onto a rotatablebase (rotatable member) 22 which is mounted on the housing 26 of thelaser-beam scanner to be rotatable about a rotational axis 16 a relativeto the housing 26. The scanning optical system shown in FIG. 1 isenclosed in the housing 26. The rotational axis 16 a extendsperpendicular to the optical axis of the cylindrical lens 16 and thedirection (path) of the laser beam L3. Note that, in this embodiment,the optical axis of the cylindrical lens 16 lies in a plane that isdefined by the scanning light beam emitted from the polygon mirror 8.

The cylindrical lens 16 can be rotated about the rotational axis 16 a todeflect the laser beam L3 which passes therethrough so as to shift thesame substantially in parallel on a plane which is perpendicular to therotational axis 16 a to thereby either delay or advance the timing ofthe incident laser beam L3 on the laser-beam detector 18. Accordingly,the timing of commencement of writing each scanning line with respect tothe photoconductive surface of the drum 1 can be adjusted by rotatingthe cylindrical lens 16.

The rotatable base 22, onto which the cylindrical lens 16 is mounted, isprovided with a disc portion 221 and a shaft 224 which is formedintegral with the disc portion 221. The rotatable base 22 is connectedto the housing 26 so that the disc portion 221 is rotatably fitted in acircular recess 222 with the shaft 224 being rotatably fitted into ahole 223 formed at the center of the bottom of the circular recess 222.With this structure, the rotatable base 22 is rotatable about the shaft224 with respect to the housing 26 so that the cylindrical lens 16 canrotate about the rotational axis 16 a.

The rotatable base 22 is provided with a circumferential slot 241 whichextends circumferentially about the rotational axis 16 a. A set screw242 is inserted into the circumferential slot 241 so that the set screw242 is screw-engaged with a female screw hole 243 formed at the bottomof the circular recess 222. The rotatable base 22 can be rotated aboutthe rotational axis 16 a on the housing 26 when the set screw 242 isloosened while the rotatable base 22 cannot be rotated about therotational axis 16 a on the housing 26 when the set screw 242 is tightlyfastened. Accordingly, the circumferential slot 241, the set screw 242and the female screw hole 243 together constitute an adjusting device 24for adjusting the rotational position of the cylindrical lens 16 aboutthe rotational axis 16 a and for fixing the same with respect to thehousing 26.

In the laser-beam scanner having such a structure, the laser beam L1emitted from the laser diode 2 is incident upon the reflected mirror 6via the collimating lens 4 a and the cylindrical lens 4 b. Subsequently,the laser beam L1 is reflected by the reflected mirror 6 to be incidentupon the polygon mirror 8. The polygon mirror 8 has a regular hexagonalcross section and is provided along a circumference thereof with sixreflecting surfaces (scanning laser beam deflecting surfaces). The laserbeam reflected by the reflecting mirror 6 to be incident on the polygonmirror 8 is reflected by each of the six reflecting surfaces while thepolygon mirror 8 rotates. The laser beam reflected by the polygon mirror8 is incident on the fθ reflecting lens 10. The laser beam L2 reflectedby the fθ reflecting lens 10 to proceed towards the fθ lens 12 passestherethrough to be reflected by the reflecting mirror 20 to therebyproceed towards the photoconductive surface of the drum 1. The laserdiode 2 is controlled to turn its laser emission ON and OFF inaccordance with given image data to draw a corresponding image(charge-latent image) on the photoconductive surface of the drum 1; andsubsequently, the image drawn on the photoconductive surface of the drum1 is transferred to plain paper according to a conventionalelectrophotographic method.

The polygon mirror 8 is rotated at a fast rotational speed in thedirection of the arrow “A” shown in FIG. 1, so that the incident angleof the laser beam. L1 on each reflecting surface of the polygon mirror 8varies. Hence, the laser beam L2 is deflected by the polygon mirror 8 inthe main scanning direction (indicated by an arrow B in FIG. 1).

The laser beam L3 which is incident on the fθ reflecting lens 10 to bereflected by the reflecting mirror 14 proceeds towards the cylindricallens 16 rather than the fθ lens 12. As described the above, when thelaser beam L3 passes through the cylindrical lens 16, the laser beam L3which proceeds towards the laser-beam detector 18 is deflected to shiftsubstantially in parallel on a plane which is perpendicular to therotational axis 16 a. Namely, when the laser beam L3 passes through thecylindrical lens 16, the laser beam L3 which proceeds towards thelaser-beam detector 18 is deflected in a direction to either delay oradvance the timing of commencement of writing each scanning line withrespect to the photoconductive surface of the drum 1.

Each time the laser beam L3 is incident on the laser-beam detector 18,the laser-beam detector 18 outputs a pulse signal. The pulse signalsoutput from the laser-beam detector 18 are input to a processor (notshown), and subsequently, the processor generates correspondinghorizontal synchronizing pulses (HSYNC) to determine the timing ofcommencement of writing main scanning data; i.e. each main scanningline.

The horizontal synchronizing pulses are input to a clock generator sothat it synchronously generates corresponding clock pulses. Subsequentlythe clock pulses are input to a memory for storing image data, and thestored image signals are sequentially read out of the memory inaccordance with the input close pulses. The laser diode 2 outputs thelaser beam L1 which is modulated in accordance with the image signalsread out of the memory.

The way of adjusting the angular position of the cylindrical lens 16 todeflect the incident laser beam so as to delay or advance the timing ofcommencement of writing each scanning line with respect to thephotoconductive surface of the drum 1 will be hereinafter discussed.

First of all, the rotatable base 22 having the cylindrical lens 16mounted thereon needs to be fitted in the circular recess 222, with theshaft 224 being fitted into the hole 223 and with the set screw 242being engaged with the female screw hole 243 through the circumferentialslot 241.

In this state, the set screw 242 is loosened and subsequently therotatable base 22 is slightly rotated clockwise or counterclockwiseabout the shaft 224, i.e., the rotational axis 16 a.

In the case where the cylindrical lens 16 is rotated clockwise as viewedin FIG. 3A from the position shown by a solid line to the position shownby a dotted line, the laser beam L3 incident on the laser-beam detector18 is deflected to shift to the left from the position shown by a solidline to the position shown by a two-dotted chain line in FIG. 3A. Whenthe polygon mirror 8 is rotated, the laser beam L3 is scanned (moved)from right to left in FIGS. 3A and 3B. Accordingly, the rotation of thecylindrical lens 16 as shown in FIG. 3A causes the laser-beam detector18 to delay the output of a pulse signal to thereby delay the timing ofcommencement of writing each scanning line with respect to thephotoconductive surface of the drum 1.

On the other hand, in the case where the cylindrical lens 16 is rotatedcounterclockwise as viewed in FIG. 3B from the position shown by a solidline to the position shown by a dotted line, the laser beam L3 incidenton the laser-beam detector 18 is deflected to shift to the right fromthe position shown by a solid line to the position shown by a two-dottedchain line in FIG. 3B. This makes the laser-beam detector 18 to advancethe output of a pulse signal to thereby advance the timing ofcommencement of writing each scanning line with respect to thephotoconductive surface of the drum 1.

After the adjustment of the timing of commencement of writing eachscanning line is completed, the set screw 242 is tightly fastened to fixthe disc portion 221 to the circular recess 222 of the housing 26, whichcompletes the adjusting operation. The cylindrical lens 16, therotatable base 22, the circular recess 222 and the adjusting device 24together constitute a light beam incident position adjusting device.

It can be appreciated from the foregoing that the incident position ofthe laser beam L3 with respect to the laser-beam detector 18 can beeasily and precisely adjusted by rotating the rotatable base 22 aboutthe rotatable axis 16 a. Hence, with the light beam incident positionadjusting device, the timing of commencement of writing each scanningline with respect to the photoconductive surface of the drum 1 can beeasily and precisely adjusted by rotating the rotatable base 22 aboutthe rotatable axis 16 a.

FIG. 4 shows an embodiment in which, so as not to relatively move, thelaser-beam detector 18′ (photo-detector and the laser diode 2′(light-beam emitter) are supported on a common circuit substrate 100. Inthis construction, since the laser-beam detector 18′ is fixed to thesubstrate 100, the type of adjusting device that moves thephoto-detector (i.e., the laser-beam detector 18′) cannot be used.However, in the above-described adjusting device of the presentinvention, the cylindrical lens 16 is rotated in order to performadjustment; therefore, the timing of the incident laser beam L3 on thelaser-beam detector 18′ can be adjusted regardless of the type ofphoto-detector being utilized.

The device for adjusting the rotational position of the cylindrical lens16 (and fixing the cylindrical lens 16 to the housing 26) is not limitedsolely to the particular aforementioned device (i.e., the adjustingdevice 24) but can be any other device as long as it bears a similarfunction. FIG. 5 shows another embodiment of the adjusting device foradjusting the rotational position of the cylindrical lens 16. In thisembodiment the housing 26 is provided on a bottom surface thereof with acircular recess 222′ which corresponds to the circular recess 222 of theprevious embodiment. A circular through hole 225 through which thecylindrical lens 16 can be inserted in the housing 26 is formed at thecenter of the bottom of the circular recess 222′. A rotatable base 22′,which corresponds to the rotatable base 22 of the previous embodiment,is not provided with a shaft which corresponds to the shaft 224 of therotatable base 22. When the rotatable base 22′ is set on the housing 26,the disc portion 221 of the rotatable base 22′ is rotatably fitted inthe circular recess 222′ with the cylindrical lens 16 being insertedinto the housing 26 through the through hole 225. With such a adjusting(fixing) device, the cylindrical lens 16 can be fixed to the housing 26in place from outside the housing 26, which makes it easier to set thecylindrical lens 16 on the housing 26.

In the aforementioned embodiments, the rotatable base 22 (or 22′) isfixed to the housing 26 using only one set screw 242. However, therotatable base 22 (or 22′) can be fixed to the housing using more thanone set screw. FIG. 6 shows another embodiment using two set screws 242to fix the disc portion 221 of the rotatable base 22 to the housing 26.FIG. 7 shows yet another embodiment using three set screws 242 to fixthe disc portion 221 of the rotatable base 22 to the housing 26. In FIG.6 the two set screws 242 are positioned on respective sides with respectto the path of the laser beam L3 so as to face respective ends (rightand left ends as viewed in FIG. 6) of the cylindrical lens 16. In FIG. 7the three set screws 242 are positioned at regular intervals in acircumferential direction of the disc portion 221.

FIG. 8 shows another embodiment of the adjusting device for adjustingthe rotational position of the cylindrical lens 16. In this embodimentthe disc portion 221 is fixed to the housing 26 by a adjusting device 30which is composed of a leaf spring 302 and two set screws 303 forsecuring the leaf spring 302 to the housing 26. The leaf spring 302 hasa substantially rectangular shape and is provided at a center thereofwith a circular hole 301 in which the cylindrical lens 16 is positioned.The longitudinal length of the leaf spring 302 is larger than thediameter of the disc portion 221 so as to press the same against thehousing 26. The leaf spring 302 is provided, on a surface thereof facingthe disc portion 221, with two projections 304 which are positioned onrespective sides with respect to the cylindrical lens 16 to be alignedalong the path of the laser beam L3, as can be seen in FIG. 8. The leafspring 302 is further provided at respective ends thereof with two slitsthrough which the two set screws are respectively inserted to be screwedinto the housing 26. In a state where the leaf spring 302 is tightlysecured to the housing 26 by the set screws 303, the two projections 304of the leaf spring 302 come into pressing contact with the disc portion221, so that the disc portion 221 is tightly held between the leafspring 302 and the housing 26, so that the disc portion 221 is fixed tothe housing 26.

FIG. 9 shows yet another embodiment of the adjusting device foradjusting the rotational position of the cylindrical lens 16. In thisembodiment the disc portion 221 is fixed to the housing 26 by aadjusting device 40 which includes a leaf spring 402 and a set screw 403for securing the leaf spring 402 to the housing 26. The leaf spring 402has a substantially U-shape and is provided with two parallel projectingportions 401 between which the cylindrical lens 16 is positioned. Theprojecting portions 401 are positioned on respective sides relative tothe path of the laser beam L3, as can be seen in FIG. 9. Each projectingportion 401 is provided, at its tip on a surface thereof facing the discportion 221, with a projection 404. In a state where the leaf spring 402is tightly secured to the housing 26 by the set screw 403, the twoprojections 404 of the leaf spring 402 come into pressing contact withthe disc portion 221, so that the disc portion 221 is tightly heldbetween the leaf spring 402 and the housing 26, so that the disc portion221 is fixed to the housing 26.

FIG. 10 shows an embodiment of device for rotating the cylindrical lens16. In this embodiment, the cylindrical lens 16 is positioned in placeby inserting the same into the housing 26 from outside the housing 26,and the operation of rotating the cylindrical lens 16 can be carried outfrom outside the housing 26.

In this embodiment, similar to the embodiment shown in FIG. 5, thehousing 26 is provided on a bottom surface thereof with a circularrecess 222′. A circular through hole 225 through which the cylindricallens 16 can be inserted in the housing 26 is formed at the center of thebottom of the circular recess 222′. The disc portion 221 of thisembodiment is provided with two circumferential slots 241 for fixing thedisc portion 221 to the mousing 26 by two set screws 242 respectivelyinserted into the two circumferential slots 241. The disc portion 221 isfurther provided with a radial slot 601 which extends in a radialdirection of the disc portion 221. The disc portion 221 is rotatablyfitted in the circular recess 222′ with the cylindrical lens 16 beinginserted into the housing 26 through the through hole 225. A tool 603 isused to rotate the cylindrical lens 16. The tool 603 is provided at thetip thereof with an engaging pin 602 which can be inserted into theradial slot 601. The axis of the engaging pin 602 extends parallel with,but deviates from, the rotational axis of the tool 603, so that the discportion 221 is rotated when the tool 603 rotates about its rotationalaxis with the engaging pin 602 being inserted into the radial slot 601.Each set screw 242 needs to be loosened in advance when the disc portion221 is rotated by the tool 603. The slot 601 and the tool 603 togetherconstitute a device 60 for externally rotating the cylindrical lens 16.

In a state where the engaging pin 602 is engaged with the radial slot601, rotating the tool 603 without moving the same in a radial directionthereof causes the disc portion 221 (the cylindrical lens 16) to rotateclockwise or counterclockwise in a direction shown by an arrow in FIG.10. Hence, with the use of the device 60, the incident position of thelaser beam L3 on the laser-beam detector 18 can be finely and easilyadjusted even from outside the housing 26 of the scanner. After theadjusting operation (i.e., the rotation of the cylindrical lens 16) iscompleted, the tool 603 is disengaged from the disc portion 221 andsubsequently each set screw 242 is tightly fastened to fix the discportion 221 to the circular recess 222′ of the housing 26, whichcompletes the adjusting operation.

FIG. 11 shows another embodiment of a device for rotating thecylindrical lens 16. In this embodiment, similar to the previousembodiment shown in FIG. 10, the cylindrical lens 16 is positioned inplace by inserting the same into the housing 26 from outside the housing26, and the operation of rotating the cylindrical lens 16 can be carriedout from outside the housing 26. The housing 26 is provided on a bottomsurface thereof with a circular recess 222′. A circular through hole 225through which the cylindrical lens 16 can be inserted in the housing 26is formed at the center of the bottom of the circular recess 222′. Thedisc portion 221 of this embodiment is provided with two circumferentialslots 241 for fixing the disc portion 221 to the housing 26 by two setscrews 242 respectively inserted into the two circumferential slots 241.The disc portion 221 is further provided on an outer peripheral surfacethereof with a circumferential gear 701. The disc portion 221 isrotatably fitted in the circular recess 222′ with the cylindrical lens16 being inserted into the housing 26 through the through hole 225. Thehousing 26 is provided with a small circular recess 226 which isconnected with the circular recess 222′. In this embodiment a tool 703is used to rotate the cylindrical lens 16. The tool 703 is provided atthe tip thereof with a pinion gear 702 which can be fitted in the smallcircular recess 226. The pinion gear 702 meshes with the circumferentialgear 701 of the disc portion 221 when the pinion gear 702 is fitted inthe small circular recess 226. Each set screw 242 needs to be loosenedin advance when the disc portion 221 is rotated by the tool 703. Thecircumferential gear 701, the tool 703 and the small circular recess 226together constitute a device 70 for rotating the cylindrical lens 16.

The pinion gear 702 is engaged with the circumferential gear 701 byinserting the pinion gear 702 into the small circular recess 226 whenthe cylindrical lens 16 needs to be rotated. In a state where the piniongear 702 is engaged with the circumferential gear 701, rotating the tool703 causes the disc portion 221 (the cylindrical lens 16) to rotateclockwise or counterclockwise in a direction shown by an arrow in FIG.11. Hence, with the use of the device 70, the incident position of thelaser beam L3 on the laser-beam detector 18 can be finely and easilyadjusted even from outside the housing 26 of the scanner. After theadjusting operation (i.e., rotation of the cylindrical lens 16) iscompleted, the tool 703 is taken out of the small circular recess 226 ofthe housing 26 and subsequently each set screw 242 is tightly fastenedto fix the disc portion 221 to the circular recess 222′ of the housing26, which completes the adjusting operation.

In each of the aforementioned embodiments, although the cylindrical lens16 as an optical member is fixed to the disc portion 221, thecylindrical lens 16 can be replaced by a plane-parallel plate to attaina similar effect. FIGS. 3A and 3B show a sectional portion of thecylindrical lens 16; the sectional portion of the cylindrical lens 16does not have any power in scanning (beam shifting) direction (right toleft in FIGS. 3A and 3B) with respect to the laser-beam detector 18. Inview of this aspect, if this sectional portion is replaced by anequivalent plane-parallel plate that does not have any power in thescanning direction, a similar beam-shifting effect as shown in FIGS. 3Aand 3B is carried out by rotating the plane-parallel plate. However, acylindrical lens 16 is used in the above-described embodiment as thecylindrical lens facilitates collection of the laser beam L3 onto thelaser-beam detector 18.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

1. A scanner comprising: a light-beam emitter for emitting a light beam;a light-beam deflector for deflecting said light beam to scan a scanningsurface; a photo-detector provided at a position outside animage-forming scanning range of said scanning surface to detect ascanning light beam before said scanning light beam starts generating ascanning line in said image-forming scanning range; a rotatable memberlocated in front of an incident surface of said photo-detector andpositioned in a recess formed on an outer surface of a housing, saidrotatable member being rotatable about a rotational axis perpendicularto a plane defined by said scanning light beam by said deflector; anoptical, member that is provided on said rotatable member, said opticalmember allowing said scanning light beam to pass therethrough to beincident upon said incident surface of said photo-detector; and a devicefor adjusting rotational, position of said rotatable member about saidrotational axis; wherein a through hole through which said opticalmember is inserted in said housing is formed at the bottom of saidrecess, and said optical member is inserted into said housing throughsaid through hole.